Liquid suspension of polyethylene oxide for use in treating paper and pulp wastewater

ABSTRACT

A flocculating agent which comprises: a particulate ethylene oxide polymer present in an amount of between about 20 to about 35% by weight; an inert liquid vehicle comprising a mixture of a glycol which is present in an amount between about 25 to about 30% by weight, and glycerine which is present in an amount between about 45 to about 50% by weight, wherein the specific gravity of the ethylene oxide polymer is approximately the same as the specific gravity of the inert liquid vehicle; and a suspension agent which is present in an amount between about 0.4 to about 0.6% by weight, wherein the flocculating agent has a viscosity in the range between about 1800 to about 5900 cps.

This is a division, of application Ser. No. 07/716,075, filed on Jun. 7,1991, now U.S. Pat. No. 5,173,208.

The present invention is directed to a unique flocculating agent and aprocess capable of improving the retention and purification of cellulosefibre suspensions, and clarification of wastewater generated from thepaper, pulp and board industries.

BACKGROUND OF THE INVENTION

Prior to delivery of paper and pulp wastewater to a dissolved airflotation (DAF) unit the wastewater is pre-treated with chemicaladditives which aid in the retention and separation of cellulose fibresuspension, fillers and other dispersed particles from the water.

In the dissolved air flotation process, clarification is achieved byforming micron-sized air bubbles in the water-fibre suspension whichattach themselves to the suspended fibre or ash and float to the surfacewhere they can be skimmed off with a mechanical scoop. The air bubblesare formed by dissolving air under 60-90 psi pressure. When released tothe atmosphere in the DAF unit, the gas comes out of solution producingbubbles which average 20 microns in size.

Another advantage of dissolved air is that the lifting action of thebubbles tends to concentrate solids at the surface often making itpossible to recover solids at concentrations of 2-4%. DAF units aretypically designed such that the aerated mixture is laid in the unit atessentially zero velocity. In circular units this is accomplished bymatching the speed of rotation of the inlet manifold to the flow. Thisminimizes turbulence and cross flow allowing the unit to take fulladvantage of coagulation, flocculation, and the lifting action of thebubbles.

Despite the inherent efficiency of DAF units and recent improvements andinnovations in design, in most cases it is desirable and cost effectiveto enhance their performance by using synthetic coagulants andflocculants. Such polymer additives can increase throughput and aid inthe removal of fillers such as clay, titanium, and calcium carbonatewhich are often in a highly dispersed state due to the charge balance ofthe influent.

Canadian Patent No. 1,004,782 discloses the use of a phenol formaldehyderesin in combination with a high molecular weight polyethylene oxide toimprove the retention at the dewatering of cellulose fibre suspensions.It was determined therein that the polyethylene oxide facilitatesagglomeration of the flocculations formed with the phenol formaldehyderesin whereby retention and clarification are facilitated.

Swedish Patent Publication No. 454,507 (assigned to Berol Kemi Ab)discloses that the retention and/or purification of cellulose fibresuspensions and clarification of wastewater within the paper, pulp orboard industry may be improved through pre-treatment with phenolformaldehyde resin and high molecular weight polyethylene oxide incombination with a cationic starch derivative or a cationic cellulosederivative.

Both of the aforementioned conventional pre-treatment methods utilize adry particulate polyethylene oxide flocculant to facilitate retentionand clarification. That is, these conventional methods call for theaddition of polyethylene oxide to wastewater by diluting dry particularpolyethylene oxide with water to approximately 0.2% by weightimmediately before addition.

The present inventors have developed a novel liquid suspension ofpolyethylene oxide which exhibits a much lower viscosity even at ahigher concentration (based on percent active), i.e., a product which ismore pumpable and which goes into solution much faster than drypolyethylene oxide. Experiments have shown that the novel liquidsuspension of polyethylene oxide demonstrated a replacement ratio of 2:1when compared to dry polyethylene oxide. It is believed that possibleexplanations for the markedly improved viscosity and flow rates ofliquid suspension of polyethylene oxide verses dry polyethylene oxideare: (1) more effective solubilization of the liquid suspension due tothe presence of a wetting agent, and (2) shear sensitivity of thepolyethylene oxide (i.e., shear degradation). That is, liquid suspensionof polyethylene oxide facilitates solution of the polyethylene oxideparticles at a faster rate and higher level of activity than theconventional dry feeder approach.

Although it has not been applied to the treatment of pulp, paper andboard industry wastewater, U.S. Pat. No. 3,843,589 (Wartman), whichissued on Oct. 22, 1974, does disclose the forming of a pumpable slurryof polyethylene oxide. According to the Wartman patent, a stable slurryformulation may be formed by mixing particulate polyethylene oxide, aninert liquid vehicle of a glycol and glycerine, and a thickening agent,e.g., colloidal silica. This patent was particularly concerned with thepumping of polyethylene oxide slurries against a head pressure usingsome type of positive displacement pump, e.g., gear pumps, moyno pumps,and diaphragm pumps. These pumping configurations can result in aphenomenon called "synaeresis", i.e., liquid carrier medium flows backthrough the clearance while the particles are not free to do so, thusresulting in the forward chamber of the pump becoming filled withsemi-dry polymer due to the backflow of the liquid carrier medium. Thisliquid suspension exhibits high resistance to stratification andmolecular weight degradation of the active polymer.

The primary difference between the liquid suspension of polyethyleneoxide according to the present invention and that disclosed in theWartman patent is that the present invention produces a flocculatingagent which is suitable for use as a pre-treating aid in paper and pulpwastewater. Moreover, the present invention utilizes a suspension agentto assist in maintaining the polyethylene oxide in suspension within theinert liquid vehicle. It also results in a liquid suspension which has amuch lower viscosity than that of Wartman, and which is better suitedfor use as a flocculant in the pre-treatment of paper and pulpwastewater.

One reason for the drastic difference in viscosity is that the Wartmanpatent discloses the use of a thickening agent, such as colloidalsilica, which does not reduce viscosity as the solids loading isincreased. To the contrary, the suspension agent used in theflocculating agent of the present invention provides for a dramaticreduction in viscosity, increased stability and an increased solidsloading.

The present invention also provides many additional advantages whichshall become apparent as described below.

SUMMARY OF THE INVENTION

A flocculating agent which comprises: a particulate ethylene oxidepolymer present in an amount of between about 20 to about 35% by weight;an inert liquid vehicle comprising a mixture of a glycol which ispresent in an amount between about 25 to about 30% by weight, andglycerine which is present in an amount between about 45 to about 50% byweight, wherein the specific gravity of the ethylene oxide polymer isapproximately the same as the specific gravity of the inert liquidvehicle; and a suspension agent which is present in an amount betweenabout 0.4 to about 0.6% by weight.

The glycol is preferably propylene glycol. The suspension agentcomprises a mixture of a polymeric fatty acid ester and a dispersingagent. Moreover, the flocculating agent has a Brookfield viscosity inthe range between about 1800 to about 5900 centipoise (cps).

The specific gravity of the ethylene oxide polymer is in the rangebetween about 1.13 to about 1.22, and the specific gravity of the inertliquid vehicle is in the range between about 1 11 to about 1.23.

An additional object of the present invention is a method of treatingpaper, pulp or board wastewater to improve retention and purification ofcellulose fibre suspensions and clarification of the wastewater. Themethod comprises the addition thereto of a flocculating agent whichcomprises a particulate ethylene oxide polymer present in an amount ofbetween about 20 to about 35% by weight, an inert liquid vehiclecomprising a mixture of a glycol which is present in an amount betweenabout 25 to about 30% by weight, and glycerine which is present in anamount between about 45 to about 50% by weight, wherein the specificgravity of the ethylene oxide polymer is approximately the same as thespecific gravity of the inert liquid vehicle, and a suspension agentwhich is present in an amount between about 0.4 to about 0.6% by weight.

The flocculating agent according to this method is used in aconcentration in the range between about 0.2 to about 0.5%, morepreferably in the range between about 0.4 to about 0.5%.

Other and further objects, advantages and features of the presentinvention will be understood by reference to the following examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Paper, pulp and board wastewater is pre-treated with a liquid suspensionof polyethylene oxide (i.e., flocculating agent) to improve retentionand/or purification of cellulose fibre suspensions, and clarification ofthe wastewater. The wastewater is typically pre-treated prior toclarification within a dissolved air flotation (DAF) unit where therecovered solids and colloidal material are floated to the surface ofthe DAF unit and skimmed off by a mechanical scoop. The resultantclarified water is thereafter sent on for further processing.

Optionally, this flocculating agent is used together with a settlingclarifier for primary clarification of effluents from a pulp or paperproduction process.

The flocculating agent comprises: a particulate ethylene oxide polymerpresent in an amount of between about 20 to about 35% by weight; aninert liquid vehicle comprising a mixture of a glycol which is presentin an amount between about 25 to about 30% by weight, and glycerinewhich is present in a amount between about 45 to about 50% by weight;and a suspension agent which is present in an amount between about 0.4to about 0.6% by weight.

The ethylene oxide polymer is preferably polyethylene oxide having amolecular weight in the range between about 100,000 to about 20,000,000,preferably about 5,000,000 to about 20,000,000, more preferably about8,000,000 to about 12,000,000.

The glycol is preferably propylene glycol. Although it is also possiblethat the glycol could also be 1,3-butylene glycol, 1,6-hexylene glycol,ethylene glycol, and dipropylene glycol. It is also possible that theglycol could be replaced with butyl carbitol.

It may also be possible to substitute any of the following compositionsfor glycerine 1,2,3,4,5,6 hexane hexol, 1,2,3,4 butane tetrol,pentaerythritol and ethylene carbonate.

The suspension agent comprises a mixture of a polymeric fatty acid esterand another dispersing agent. An example of a preferred polymeric fattyacid ester is a 40% polymeric fatty acid ester, e.g., Atkemix HypermerLP6 sold by ICI. The Atkemix Hypermer LP6 fatty acid ester is preferablycombined with another dispersing agent such as Atkemix Hypermer PS2 soldby ICI. Other potential dispersing agents are stearic monoethanolamide,N,N'-ethylene bis stearamide, polyacrylic acid, polyacrylate, andaluminum stearate. The suspension agent provides improved wetting,dispersion, stabilization and fluidization which can give rise to avariety of effects which may be used to advantage in many particulatesuspensions. The effects of the suspension agent on the liquidsuspension of polyethylene oxide is a dramatic viscosity reduction,increased stability and increased solids loading, i.e., can attainhigher percent by weight polyethylene oxide than conventionalpolyethylene suspensions.

The flocculating agent has a Brookfield viscosity in the range betweenabout 1800 to about 5900, and more preferably 1800 to about 3200 cps.The specific gravity of the ethylene oxide polymer is approximately thesame as the specific gravity of the inert liquid vehicle. Specificgravity of the ethylene oxide polymer is in the range between about 1.13to about 1.22, and the specific gravity of the inert liquid vehicle isin the range between about 1.11 to about 1.23.

The preferred flocculating agent is prepared by initially charging areactor vessel with 27.6% by weight of a propylene glycol and 47% byweight of a 95% solution of glycerine with agitation. Cool the mixtureto approximately 15°-25° C., more preferably between about 18°-22° C.The use of temperatures above 25.C can result in products which are moreviscous than desirable. During mixing, accurately charge the reactorvessel with a suspension agent comprising 0.2% by weight of a 40%polymeric fatty acid ester and 0.2% by weight of a dispersing agent.Continue to mix rapidly and slowly charge the reactor vessel with 25% byweight of a dry particulate polyethylene oxide. If added too rapidly,the polyethylene oxide tends to form lumps in the batch which aredifficult to break up with mixing. After all of the polyethylene oxideis charged into the vessel, mix for an additional hour.

The flocculating agent prepared above is used in treating paper, pulp orboard wastewater to improve retention and purification of cellulosefibre suspensions, and clarification of the wastewater. The flocculatingagent is preferably added to the wastewater in a concentration withinthe range between about 0.2 to about 0.5%, more preferably in the rangebetween about 0.4 to about 0.5%. This is accomplished by adding theflocculating agent to water in a mixing vessel having a blade type ofagitator which is capable of operating at between 350-400 rpm.

The following comparative examples where conducted to demonstrate theadvantages of the liquid suspension of polyethylene oxide accordingverses the conventional dry polyethylene oxide preparations and todetermine the best formulation of the product.

EXAMPLES 1-4

Four samples were prepared and tested for viscosity and flow rate.Sample 1 is a 0.1% solution of polyethylene oxide prepare from dryparticulate polyethylene oxide. Sample 2 is a 0.2% solution ofpolyethylene oxide prepared from dry particulate polyethylene oxide.Sample 3 is a 0.4% solution of polyethylene oxide prepared from a liquidsuspension of polyethylene oxide (i.e., flocculating agent) comprising27.6% by weight of propylene glycol, 47% by weight of a 95% solution ofglycerine, 0.2% by weight of a 40% solution of a polymeric fatty acidester, 0.2% by weight of a dispersing agent, and 35% by weight of a dryparticulate polyethylene oxide. Sample 4 is an 0.8% solution ofpolyethylene oxide prepared from the liquid suspension of polyethyleneoxide describe in sample 3 above.

The results are set forth in Tables 1 and 2 below.

                                      TABLE 1                                     __________________________________________________________________________    [Viscosity Profile @ 350 rpm]                                                 SAMPLE                                                                              30 sec                                                                            60 sec                                                                            120 sec                                                                           5 min                                                                             10 min                                                                            15 min                                                                            20 min                                                                            25 min                                                                            30 min                                  __________________________________________________________________________    1     4.9 11.9                                                                              8.5 8.0 8.5 8.1 8.5 8.4 8.3                                     2     5.2 6.1 6.9 7.0 8.0 8.4 8.5 8.6 9.0                                     3     66.5                                                                              78.4                                                                              23.5                                                                              13.5                                                                              12.0                                                                              12.1                                                                              12.0                                                                              12.0                                                                              12.0                                    4     88.0                                                                              192 46.9                                                                              44.1                                                                              40.1                                                                              39.6                                                                              39.5                                                                              39.5                                                                              39.4                                    __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    [Flow Rate: Time for 20 mL to flow through a pipette]                         SAMPLE                                                                              30 sec                                                                            60 sec                                                                            120 sec                                                                           5 min                                                                             10 min                                                                            15 min                                                                            20 min                                                                            25 min                                                                            30 min                                  __________________________________________________________________________    1      30.4                                                                              40.3                                                                             40.8                                                                              36.9                                                                              35.6                                                                              31.5                                                                              31.1                                                                              30.8                                                                              30.6                                    2      32.7                                                                              33.7                                                                             33.5                                                                              32.3                                                                              32.2                                                                              32.9                                                                              33.2                                                                              31.3                                                                              31.7                                    3     173.4                                                                             148.1                                                                             84.2                                                                              50.4                                                                              46.0                                                                              45.9                                                                              46.4                                                                              45.4                                                                              44.7                                    4     408.0                                                                             305.7                                                                             247.0                                                                             156.0                                                                             111.1                                                                             89.7                                                                              79.2                                                                              71.9                                                                              62.8                                    __________________________________________________________________________

A lot of insoluble polymer was discovered in beakers of samples 1 and 2after 30 minutes. Also, it was determined that the liquid suspension ofpolyethylene oxide in samples 3 and dissolved much faster than the drypolyethylene oxide used in samples 1 and 2. The viscosity of sample 3was substantially lower than either of samples 1 or 2, based onconcentration.

EXAMPLES 5-13

The following samples were prepared in accordance with theabove-mentioned liquid suspension polyethylene oxide make-up procedure.Samples 5, 6, 7, 9, and 13 remained stable after three days at 60° C.,while samples 8, 10, 11, and 12 exhibited a slight separation.

                  TABLE 3                                                         ______________________________________                                                                   Heavy  Carbopol                                                    Isoparaffinic                                                                            Aromatic                                                                             934 (poly-                                  Sample                                                                              Glycerine Solvent    Naptha acrylate)                                                                             PEO                                 ______________________________________                                        5     70        5          --     1       15                                  6     70        10         --     1       15                                  7     70        --         5      1.8     15                                  8     70        5          --     0.5     15                                  9     70        5          --     0.8     15                                  10    75        --         --     0.8     15                                  11    80        --         --     0.8     20                                  12    75        --         --     0.8     25                                  13    70        5          --     0.8     25                                  ______________________________________                                    

None of the aforementioned compositions produced a flocculating agenthaving the retention and clarification characteristics of thepolyethylene oxide prepared in accordance with sample 3 above.

EXAMPLE 14

In order to improve the stability of the liquid suspension ofpolyethylene oxide made in accordance with the aforementioned method, a1 liter sample was prepared from:

27.5% (275 grams) of propylene glycol

47.0% (470 grams) of 45% glycerine

25.0% (250 grams) of a dry polyethylene oxide

0.5% (5 grams) of a 40% polymeric fatty acid ester suspension agent

Stability of the suspension was improved by the matching of the specificgravity of the polyethylene oxide and the combination of propyleneglycol/glycerine.

EXAMPLES 15-28

The following examples were an attempt to determine the proper amount ofsuspension agent which can be added to the liquid suspension ofpolyethylene oxide without making the suspension unstable.

The liquid suspension set forth in Table 4 below contained 20% by weightof dry polyethylene oxide, 29.5 % by weight of propylene oxide, 50.5% byweight of 45% glycerine, and varying amounts of a suspension agent,i.e., 40% polymeric fatty acid ester.

                  TABLE 4                                                         ______________________________________                                        Sample  % PEO      % Suspension Agent                                                                          Viscosity                                    ______________________________________                                        15      20         0             1300                                         16      20         0.1           2550                                         17      20         0.2           2850                                         18      20         0.3           3100                                         19      20         0.5           3050                                         ______________________________________                                    

The suspensions listed in Table 5 below included 25% by weight ofpolyethylene oxide, 27.5% by weight of propylene glycol, 47.5% of 45%glycerine, and varying amounts of suspension agent, i.e., a 40%polymeric fatty acid ester.

                  TABLE 5                                                         ______________________________________                                        Sample  % PEO      % Suspension Agent                                                                          Viscosity                                    ______________________________________                                        20      25         0             4400                                         21      25         0.1           5500                                         22      25         0.2           4500                                         23      25         0.3           4900                                         24      25         0.5           4900                                         25      25         0.6           4500                                         26      25         0.7           3500                                         27      25         0.8           3500                                         28      25         0.9           3500                                         ______________________________________                                    

Samples 15-18, 20-23 and 27-28 were not stable. Samples 25 and 26exhibited slight separation. And samples 19 and 24, both of whichincluded 0.5% by weight of a suspension agent of 40% polymer fatty acidester, appeared stable. As such, samples 19 and 24 were consideredsatisfactory liquid suspensions of polyethylene oxide. It was laterdiscovered that by combining the polymeric fatty acid ester with anotherpolymeric dispersants such as Atkemix Hypermer PS2 that stableflocculating agents can be prepared from a suspension agent present inthe range from about 0.4 to about 0.6% by weight.

EXAMPLES 29-33

The samples set forth below in Table 6 appear to demonstrate that liquidsuspensions of polyethylene oxide can be prepared with dry polyethyleneoxide in amounts of 30% or more, although such flocculating agents arenot as stable as those prepared with lesser amounts of PEO.

                  TABLE 6                                                         ______________________________________                                                      %                 %                                                   %       Propylene %       Suspension                                    Sample                                                                              PEO     Glycol    Glycerine                                                                             Agent   Viscosity                             ______________________________________                                        29    30      26        44      0.5     7500                                  30    30      26        44      0.6     7500                                  31    30      26        44      0.7     7500                                  32    30      26        44      0.8     8000                                  33    30      26        44      1.0     8000                                  ______________________________________                                    

EXAMPLE 34

A flocculating agent was prepared which comprised 27.6% by weight ofpropylene glycol, 47% by weight of glycerine, 25% by weight of drypolyethylene oxide, 0.2% by weight of a polymeric fatty acid ester(Hypermer LP6), and 0.2% by weight of another dispersing agent (HypermerPS2). This flocculating agent demonstrated a viscosity at 125° C. of1800 cps with a specific gravity of 1.153 and 2200 cps with a specificgravity of 1.147

It was determined after review of all of the aforementioned data thatthe best formula for producing a stable liquid suspension ofpolyethylene oxide includes an inert liquid vehicle comprising propyleneglycol and glycerine, dry polyethylene oxide, and a suspension agentwhich comprises a polymeric fatty acid ester and another dispersingagent; wherein the specific gravity of the dry polyethylene oxidematches the combined specific gravity of the propylene glycol and thedispersing agent. This flocculating agent has a viscosity in the rangebetween about 1800 to about 5900 cps, more preferably in the rangebetween about 1800 to about 3200 cps.

While we have shown and described several embodiments in accordance withour invention, it is to be clearly understood that the same aresusceptible to numerous changes apparent to one skilled in the art.Therefore, we do not wish to be limited to the details shown anddescribed but intend to show all changes and modifications which comewithin the scope of the appended claims.

What is claimed is:
 1. A method of treating paper, pulp or boardwastewater to improve retention and purification of cellulose fibresuspensions and clarification of said wastewater, which comprises theaddition thereto of a flocculating agent comprising a particulatepolyethylene oxide having a molecular weight in the range between about100,000 to about 20,000,000 said polyethylene oxide being present in anamount of between about 20 to about 35% by weight, an inert liquidvehicle comprising a mixture of a glycol which is present in an amountbetween about 25 to about 30% by weight, and glycerine which is presentin an amount between about 45 to about 50% by weight, wherein thespecific gravity of said polyethylene oxide is approximately the same asthe specific gravity of said inert liquid vehicle, and a suspensionagent comprising a mixture of a polymeric fatty acid ester and a seconddispersing agent selected from the group consisting of stearicmonoethanolamide, N,N'-ethylene bis stearamide, polyacrylic acid,polyacrylate and aluminum stearate, said suspension agent being presentin an amount between about 0.4 to about 0.6% by weight, wherein saidflocculating gent has a viscosity in the range between about 1800 toabout 5900 cps.
 2. The method according to claim 1 wherein the viscosityis in the range between about 1800 to about 3200 cps.
 3. The methodaccording to claim 1 wherein said flocculating agent has a concentrationin the range between about 0.2 to about 0.5%.
 4. The method according toclaim 3 wherein the concentration is more preferably in the rangebetween about 0.4 to about 0.5%.
 5. The method according to claim 1wherein said glycol is propylene glycol.
 6. The method according toclaim 1 wherein the molecular weight of said polyethylene oxide is morepreferably in the range between about 5,000,000 to about 20,000,000. 7.The method according to claim 1 wherein the specific gravity of saidpolyethylene oxide is in the range between about 1.13 to about 1.22. 8.The method according to claim 1 wherein the specific gravity of saidinert liquid vehicle is in the range between about 1.11 to about 1.23.